A key descriptor associated with the term cerebral palsy is "the disordered development of movement and posture, resulting in activity limitation." The term "movement disorders" is now commonly used to describe a range of observed abnormal movements and postures displayed by children with chronic neurological conditions, of which cerebral palsy (CP) is the most common. These children have muscle tone abnormalities related to non-progressive damage to motor pathways, in particular those contained within the cortex, basal ganglia and thalamus. In recent years there has been much focus on understanding and treating abnormal tone and movements in children with CP, including spasticity and dystonia. Spasticity, which occurs in approximately 90% of children with CP is defined as the velocity-dependent resistance of a muscle to stretch. In general, spasticity is elicited during a standard clinical examination, such as by passive range of joint motion performed at varying speeds.